Warped Hoop - Head Gravity

The recently launched Head Gravity series of tennis rackets are really soft and arm friendly. 

This rare flex got many players on board, especially previous users of the Babolat Pure Drives and Aero Pros.

However, their feedback has been mixed. Some loved the Gravity while many others hated its inconsistency and lack of accuracy.

In stock form, I find the power and stability lacking.

However, it is the incredibly soft hoop that poses the biggest problems. It is almost as soft as the old but very popular Head Prestige.

Maintaining hoop shape while stringing this Gravity is challenging. I received so many badly warped hoops that rendered the racket unplayable.

Take a look yourself at the three videos below...

The stringjob in this first video was done by another stringer. You can see the Head logo stenciled. The hoop was approximately 24.8cm wide.

In the second video below, the hoop width was approximately 25.3cm after the strings were cut and removed.

 

 
The third video showed the width to be almost exactly 25.3cm after I restrung it. No stencil. Almost zero distortion.

Naturally, the player loved the distortion free stringjob.

If you have a Head Gravity playing inconsistently, it could be the stringing. Try measuring the hoop width without and with strings.

PS: Sorry about the lousy video quality...somehow it deteriorated after uploading
 



   

Warped Hoop - Wilson Blade 104 (2013)

Almost all soft hoops rackets sent in to me were strung warped by their stringers.

This Blade 104 has a very soft flex of RA59.

The one with red strings was strung by me about a week ago. The one with black strings was strung by something else. 

The one with black strings has its hoop widened by 5mm. That is a lot!

Both rackets inside hoop width were 26.1cm when strings were cut.

Videos below...

    

Another Warped Head Prestige...

A chap I met recently named "MB" asked me to restring two Head Graphene Prestige S.

When MB first handed me the rackets, I immediately noticed how warped the hoops were. (Link)

The Head Prestige series have very soft hoops. That contributes their signature feel and flex. However, this soft hoop also makes it very challenging to tension properly while maintaining the hoop shape.

When strung wrongly, the hoop narrows and racket length lengthens. This greatly reduces the sweet spot size and also "shifts" the sweet spot downwards nearer the handle.

What one feels with a wrongly strung Prestige is what I would deem "hoop wobble" - a combination of vibrations and frame twisting mixed together during ball impact. 

The racket also becomes very difficult to play with, and almost impossible to volley with.

When tensioned and strung well, the entire frame is very smooth and quiet. The hoop is incredibly stable and the true flex of the racket at the throat area surfaces. An incredibly sweet and addictive frame to play with!

I'll let the pics below do the talking. Note there is some parallax error in the pics. The correct readings are written in blue...

Below pics from racket #1, with snapped old strings, cut out old strings and newly strung, respectively from left to right.

Below pics from racket #2, with old strings intact, cut out old strings and newly strung, respectively from left to right.

Below pics shows a side by side comparison of the hoop shape and width of racket #1 freshly strung (left) and #2 with old strings (right). Even with the naked eye, the discrepancy is visible.

Sometimes when choosing rackets, the challenge is not just whether one can handle the frame. You need to take into consideration if your stringer can string the frame properly too.




     

Exploding Woody - 1980s Slazenger Vilas International

Someone requested me to string an old wood racket and I turned it down immediately. Most woodies are at least 30+ years old. No one could predict how it would turn out.

But he insisted. So I asked for payment in advance, and his written full disclaimer, absolving me of any blame in the event of any damage.

It was the Slazenger Vilas International (link1)(link2).

A quick search online shows someone asking for US$254 for one on Ebay (link).

The racket was unplayed and in near mint condition. No scratches, nor chips nor scrapes could be found anywhere. Even the original plastic wrap was still on the handle!

Although unstrung, I could see it had been strung before. Some string cuts could be seen at the throat grommet.

Since it was not intended for serious play, I suggested stringing it with full synthetic gut at 38 lbs. That would significantly reduce hoop stress and hopefully preserve the frame intact. He agreed.

It was smooth sailing installing and tensioning the mains. Some very slight "creaks" sounds was heard while tensioning the outer mains. So I paused for a few minutes.

(If you observe the above pic carefully, you could see the laminate fracturing at the bottom right corner of the picture.)

After ascertaining the squeaking stopped and everything was intact, I continued slowly, completed the mains, then tied-off on the short side. For wood frames, that would the side with the zig-zag on top of the frame.

(Despite the dangers explained, the owner asked for one-piece stringing.)

With the long side, I started weaving the crosses from bottom-up. This was the standard pattern for one-piece stringing with wood frames.

I was tensioning the 8th cross from the bottom when there was a sudden loud snapping sound. 

But I could not see any damage nor distortion anywhere. Nevertheless, for my own safety, I stepped out of the room and observed from the door way.

An exploding racket hoop is any stringers' nightmare. Although tales have been told of it, none have seen it happen, nor could provide any evidence of it. 

Could it happen to me this time? I wondered...

Mere seconds later, the side of the hoop gave way outwards!!!

I removed the clamps immediately to release the tension! Then more loud snapping sounds...

But it was too late. The damage was done. A beautiful vintage frame completely ruined.

I could not bear to see the frame explode, so I cut out the strings.

To anyone wanting to re-string an old woody, even if it seemingly appears perfectly intact, my advice is don't. 

It is just too much risk.




     

Racket Cleanliness

After 18 months of incessant testing of new strings, an old friend, PK (link), got in touch again. He wanted to try proportional stringing with full poly. (link)

So he handed me his Babolat APD which he bought used, for a very good deal. However, the racket was so dirty.

Perhaps ingrained by my mentor many many years ago, I instinctively cleaned up the frame using an old toothbrush and rag.

Then I inspected the racket. And found two hairline cracks at the throat area, previously buried under all the dirt and grime. It doesn't show up well in the pics below, but yes, they are cracks.

Could this be why my mentor always insisted I clean rackets before working on them? I have no idea. Neither any way to check with him now.

After obtaining the green light to proceed from PK, I cut out the old strings, measured all the variables, then started work.

To me, it sure felt better working on a clean racket. The more important lesson though, is to always check used frames carefully before buying them. Clean them first if possible.

Fortunately, the cracks are very minor. It should remain playable for a good while more.

Playtest:
- After playing with it for 3 hours with his regular partners, PK was full of praise for proportional stringing. 
- In his words, he wrote:

"Yo, here is my verdict. Spin, power, comfort and control were all superb..."

- And this was what he wrote about what his playing partners commented:

"They say the spin control really good" and "A lot of pace".

- Downside was he felt he needed to make some adjustments to his grip, swing and serve. But overall, he was very satisfied.
- I replied that I had expected the adjustments because the spin-to-power ratio of this setup was very different from his regular setup of full poly. If he felt no difference and needed no changes, then why should I spend SO MUCH more time stringing his racket proportionately?
- Somehow, I get the feeling that PK is going to be asking ONLY for proportional stringing from now on...




     

Deliberate Hoop Warp

After stringing for while, I realized that some "conventional rules" could actually be bent. Some completely ignored.

Most basic of all, is the mandate to preserve the shape of the racket hoop after stringing. 

I had some brushes with hoop distortion due to my unorthodox attempts, but also encountered them when the same rackets were professionally strung. (link1)(link2)(link3)

So? What matters? 

Ultimately it's how the sticks and strings perform after they were strung. So I did up a pair - same rackets, same specs, same strings and same tension. Just to experience how different they play!

The normal one was done first. Straightforward string job, no problems.

The other one was intended to be "compressed shorter but wider". So I mounted the racket but left one mounting posts completely loose and untightened! Just to let the racket shorten when the mains were tensioned.

With the super soft hoop of the Black Ace 98, this experiment was easy.

This was the normal one at 329 mm and 245 mm.

Below was the distorted one at 324 mm and 250 mm.

From stringbed frequency measurements, the distorted frame registered a higher pitch by about 37 hz. This represents the amount that would drop overnight with no play, so it was significant.

To ensure the shortened racket had the same swingweight, a 4 grams dampener was used whereas the normal racket was dampened by rubberbands weighing 0.5 grams.

Some online folks claimed that shortened and widened hoops play better with a slightly larger sweetspot due to the elongated cross strings. I did not experience it.

Power and control felt close, with the distorted one slightly lowered-powered. Spin also felt similar.

The only significant difference I picked up seemed to be comfort. With or without dampeners, there was more dull vibrations coming from the distorted frame during off-centred hits.

A minor difference was the distorted frame seemed to flex less, especially when I was in the perfect position ready to unleash a winner. I could not be sure of this though.

By any standard, 5 mm is a significant distortion. I have cut strings out and re-done them even with 4 mm distortions. Given how little differences I felt, I may need to re-evaluate my hoop distortion tolerances. 

But before I do that, I suspect a hoop narrowing is more damaging. (link) I may need to re-do this experiment.




     

Frame Movements while Stringing

A picture speaks a thousand words.

Since I did not take any pics in my previous post (link), I snapped some while re-stringing my ProKennex Black Ace 98 with synthetic gut recently.

Below measurement was after the mains were done.

To reduce parallax error, some pics were taken from directly above the inside hoop. It spans from 1.0 cm to 26.1 cm, yielding an internal hoop width of 25.1 cm. Note the crosses were unfilled.

Here's how it looked after the crosses were completed. Racket still mounted.

From 1.0 cm to 25.4 cm, it's now 24.4 cm. The hoop narrowed 0.7 cm after the crosses were done.

The unstrung internal hoop width was 24.5 cm for this racket. So it's a 1 mm distortion.

As I mentioned in my previous post (link), my belief is no mounting would completely stop the frame from distorting. It serves more as a guide than "locking down" the hoop. 

Choosing an appropriate combination of strings, tension and stringing method should take greater emphasis.

Making a Racket Lighter?

Someone asked if I could somehow modify his racket and make it lighter. It was a vintage stick he had used since his younger days.

Although he could barely handle the weight now, playing just half hours with it intermittently, he remained deeply attached to them.

His story of how the sticks came to his possession was touching. And he was both willing to spend, and assume the full risk of possibly damaging one of the racket. Seeing how eager he was, I decided to give it a try despite low percentages of success.

He preferred to remain anonymous, so pictures and details would be limited.

The racket was so worn, I have absolutely no clue what make or brand it was. With the very head light balance, my suggestion was to try our luck to hunt for some embedded lead under the grip.

Before proceeding, I warned him:
(1) the foam pallet would be destroyed,
(2) modifying the weight would change the balance, feel and sweetspot location, and
(3) because of the changes, he would need to "rediscover" his strings and tension setups from scratch.

After removing the grip and destroying the already crumbling foam pallet, we were delighted to find two pieces of lead embedded in the graphite hairpin handle. 

We dug them out carefully and were surprised it weighed SO MUCH!

22 grams of lead! Wow!

A little weight was also trimmed from shaving the grommet and bumper guard. Some weight was re-distributed to achieve the balance he wanted.

Finally, a very thin 18 gauge string was used to re-string his racket. That saved another 3 grams compared to the earlier 15 gauge string, lowering the swingweight by approximately 3 to 5 points.

This was a rewarding endeavor for both him and me.

Taboo Stringing: Re-do Mains Only (3 & 9 mounting)

Countless have restrung only the crosses of a used stringbed successfully. 

But I have yet to hear about successful restringing of mains only. A previous post (link) explained why it could not be done.

Then I thought, instead of anchoring the main supports at 12 & 6 o'clock of the racket hoop, would it be possible if mounted at 3 & 9 instead?

That would prevent the crosses from compressing and distorting the frame width once the mains are cut, wouldn't it? 

From this perspective, doesn't it seem like the "crosses" were being strung instead?

First 2 pics below was width measurement before the above mains restring. Next 2 pics below was after.

Before:

After:

While the frame width maintained its exact measurement after the mains restring, it is important to note that the width still compressed about 6-7mm from an unstrung state. (The most extreme distortion I witnessed for this frame was a narrowing of about 11-12mm).

Even though the mains did not snap, this warp occurred because tension loss and string creep caused greater elongation in the main strings than the crosses. 

Nevertheless, if this works out, I believe there could be huge implications on how rackets could be restrung, as long as one understands and accepts the risks.


Playtest:
- The first impression was how much tighter the mains felt compared to how it last played.
- The mains dominated the feel of ball impacts. It was nice to feel it pocketing and supporting the ball as the stringbed depresses before rebounding accurately.
- Although this sounds odd, but compared to the more commonly felt feeling of the crosses supporting most of the impact, having the mains do the bulk of the work was way better! I enjoyed this tremendously!
- For this to happen, clearly, the crosses have lost a fair bit of string tension. But still, there was no instance of any odd rebound angle nor trampoline.
- If you try to imagine a freshly strung racket with the main strings about 10-15 lbs tighter than the crosses, that's probably how this felt like to me.
- Control and confidence improved. I felt more at ease just taking full relaxed swings instead of holding back with the previous worn main strings.
- String bite, feel and spin improved significantly over the old mains.
- For second serves, both sidespin and topspin curled the ball down much faster than anticipated, causing many to land short, almost right in the middle of my opponent's service box, before kicking up. So we knew spin increased.
- Sweetspot size felt the same. Likewise, shots hit off-sweetspot did not feel more or less harsh, nor extra low-powered.
- Frame width maintained the same after an hour of play.

0.6mm Dyneema Fishing Line + Syn Gut

Since the thin fishing lines kept snapping, we decided to try something stronger. The next step up would be Dyneema/ Spectra braided fishing lines.

We selected the pre-stretched spool. Even at 0.6mm, the breaking strength was rated at 150 lbs! So it's thinner and stronger.

In addition, this eight strand braided has a coefficient of friction of only 0.09, which is as slick as the most slippery poly strings we have. Another plus for spin! 

Stringing it was challenging, as usual, since it was not designed to be used in a tennis racket. Clamps slippage was the major issue. Nevertheless, I got the job done. Just an extra dose of patience and time was needed.

Take a look how fine the line was at 0.6mm, compared to the 1.25mm syn gut it was paired with.

Playtest:
- Initial hits felt very good. The thin line provided impressive feel with very good bite and spin.
- Shots that I feared hitting out previously were executed with the perfect amount of spin to curl it down instead of flying out.
- Serves could be powerful or spinny depending how I hit it.
- However, the joy was short-lived. 
- Despite further pre-stretching before stringing, the dyneema line still elongated a lot with every ball impact.
- After about 50 hits, including several serves, the stringbed became exceptionally loose. "Floppy" would be an appropriate word to describe it.
- Not only that, the hoop warped so much that the width compressed about 1cm or more. Afraid that the frame may crack (since I tensioned it quite high), I snipped the crosses immediately to release the pressure.
- Dyneema is still better reserved for fishing.

Why Not Restring Mains Only?

All the times that I restrung only the mains did not end up well. Either the stringbed developed heavy vibrations, or there was a sense of loss of control.

Now that I am testing fishing line fervently, and that the thin fishing line snaps so frequently, the question that kept popping up was, "Why not restring only the main strings after it snaps?"

The sole reason is racket warp. Once deformed, a lot of other variables are affected, such as, length, width, swingweight, sweetspot size, sweetspot location, pocketing, and feel.

Take a look for yourself...

On the left below was the freshly strung fishing mains with syn gut. On the right, the fishing mains snapped at two locations after about an hour of play. Compare the shape, length and width of the racket hoop. 

In the right picture, the racket hoop has narrowed and lengthened. Since the mains snapped, there was no tension holding together 12 and 6 o'clock anymore. The crosses compressed the hoop at 3 and 9 o'clock together, narrowing the frame.

As soon as I got home, I measured the frame width.

Just like that, the hoop narrowed by 9mm, which was huge!

I tried. No amount of re-tensioning on the mains could restore the frame back to its original shape.

So re-stringing mains only cannot, and should not be done.

Some Failed Attempts with Fishing Line

Up till now, fishing line remains the most challenging string I have worked with. 

Many friends and playing partners dismissed me as crazy until they had a go with my rackets. Then some got hooked as well!!!

If you have not tried it, don't start. Once hooked, it is very difficult to accept any other strings.

Maybe some of my failures below could act as a deterrent?

The initial problem was poor tension holding, which was solved by some ridiculous pre-stretch before stringing. Then the line kept snapping during tensioning or tie-offs.

So I tried using fishing crimps instead of tying knots. Unfortunately, that did not work well. Some crimps slipped, some snapped the string, some did not sit down well after crimping while others slid through the grommet hole.

To overcome the constant snapping, I tried a "divide and conquer" strategy. The 12 centre mains were divided into 3 pieces of 4 mains each, resulting in 6 knots, hopefully, to mitigate the amount of re-work if/when each line snaps.

However, the tension loss during tie-offs was more severe than anticipated, despite adding 15 lbs per tie-off. This, in turn, caused uneven pressures between the mains and crosses.

Above, the left racket (note the six orange knots) width was 25.3cm and the right, 26.3cm. The sweetspot disappeared for the left racket, just like this case (link).

This is why flexible hoops are a little more difficult to string well compared to stiff hoops.

The line was cut out immediately and re-strung. Back to a more conventional two tie-off knots this time.

There's some parallax error in the pic above, but the width read 26.3cm after the restring. It took me just two attempts before succeeding this time. Not too bad.

All in all, about four hours was spent pursuing this. 

Still keen to try fishing line?


20May2014 update:
- The racket in the last picture above was strung with fishing line mains and a shaped-poly cross.
- It was a bad decision as the mains snapped in just 30 minutes of play, severely notched by the sharp poly edge.

Racket Distortion after Stringing

When I mentioned to some folks about how two of my ProStaff Classics (RA72 stiffness) distorted after stringing, few believed me. They thought it was impossible and that I was crazy and just being picky! It was a pity I did not take pics then. 

One racket lengthened by 9mm and the sweetspot totally disappeared. When I brought it back, the stringer simply dismissed it as "manufacturing tolerances". That was one of the first few brushes that drove me to buy my own stringing machine.

History keeps repeating. Names withheld, two matched ProKennex Black Ace 98s suffered the same fate as my ProStaff Classic.

The chap (named DL) met up with me and asked why was one of his racket totally unplayable.

Let the pics below speak...

The top racket had yellow mains, bottom one had blue mains. 

Both DL and myself tested the rackets. The hoop length of the racket with blue mains was compressed 12mm shorter. Take a look at the last pic above, near the words "Precision".

That's why I usually measure and check the hoop length and width before and after stringing (link1)(link2). If the difference exceeds 5mm, I usually cut and re-do everything from scratch.